Small cars do poorly in collisions with midsize cars: IIHS

by Jil - April 14, 2009

Arlington, Virginia – Very small cars generally can’t protect people in crashes as well as bigger, heavier models do, according to new crash tests conducted by the U.S. Insurance Institute for Highway Safety (IIHS).

The Institute conducted three front-to-front crash tests, each involving a micro- or minicar into a midsize model from the same manufacturer, to show how extra vehicle size and weight enhance occupant protection in collisions. The IIHS said the tests are about the physics of car crashes.

“There are good reasons people buy minicars,” said Adrian Lund, IIHS president. “They’re more affordable, and they use less gas. But the safety trade-offs are clear from our new tests. Equally clear are the implications when it comes to fuel economy. If automakers downsize cars so their fleets use less fuel, occupant safety will be compromised. However, there are ways to serve fuel economy and safety at the same time.”

The tests used pairs of 2009 models from Daimler, Honda and Chrysler, because these automakers have micro and mini models that earn good frontal crashworthiness ratings based on the IIHS’ offset tests into a deformable barrier. Researchers rated performance in the 40 mph (64 km/h) car-to-car tests, based on measured intrusion into the occupant compartment, forces recorded on the driver dummy, and movement of the dummy during the impact.

The IIHS found that the Honda Fit, Smart Fortwo and Toyota Yaris rated “good” in the frontal offset barrier test, but all three rated “poor” in frontal collisions with midsize cars. The results reflect the laws of the physical universe, the Institute said, specifically principles related to force and distance. The death rate per million 1- to 3-year-old minis in single-vehicle crashes during 2007 was 35, compared with 11 per million for very large cars. Even in midsize cars, the death rate in single-vehicle crashes was 17 per cent lower than in minicars. The lower death rate is because many objects that vehicles hit aren’t solid, and vehicles that are big and heavy have a better chance of moving or deforming the objects they strike, dissipating some of the force of the impact.

“Though much safer than they were a few years ago, minicars as a group do a comparatively poor job of protecting people in crashes, simply because they’re smaller and lighter,” Lund said. “In collisions with bigger vehicles, the forces acting on the smaller ones are higher, and there’s less distance from the front of a small car to the occupant compartment to ‘ride down’ the impact. These and other factors increase injury likelihood.”

The IIHS also said that some people claim that minicars are easier to manoeuvre and so their drivers can avoid crashes in the first place, but the frequency of claims filed for crash damage is higher for mini four-door cars than for midsize ones.

In the Honda Accord versus the Honda Fit, the structure of the Accord held up well, with all measures of injury likelihood recorded on the dummy’s head, neck, chest and both legs rated “good” but one. In contrast, injury measures on the dummy in the Fit were “marginal” on the left lower leg and right upper leg, and “poor” on the right tibia, indicating a high risk of leg injury in a real-world crash of similar severity. The dummy’s head struck the steering wheel through the airbag, and intrusion into the Fit’s occupant compartment was extensive. The Fit rated “poor” in the front-to-front crash, despite its “good” worthiness based on IIHS testing into a deformable barrier. The Accord rated “good” on both tests.

In a crash between a Mercedes-Benz C-Class and Smart Fortwo, the Smart became airborne and turned 450 degrees, contributing to excessive movement of the dummy during rebound. There was extensive intrusion around the dummy from head to feet, the instrument panel moved up and toward the dummy, and the steering wheel was displaced upward. Multiple measures of injury, including leg and head, were rated “poor.” The C-Class held up well, with little to no intrusion into the occupant compartment, and nearly all measures of injury likelihood were in the “good” range.

Between the Toyota Camry and Yaris, there was far more intrusion into the occupant compartment of the Yaris than the Camry, and the Yaris’ door was largely torn away. The driver seats in both cars tipped forward, but only in the Yaris did the steering wheel move excessively. The heads of both dummies struck the steering wheels through the airbags, but only the head injury measure on the Yaris dummy rated “po0r,” and there was extensive force on the neck and right leg, plus a deep gash at the right knee. The Yaris earned an overall rating of “poor” in the car-to-car test, while the Camry rated “acceptable.”

The president of smart USA, Dave Schembri, disputed the IIHS’ findings. “This non-standard crash test performed by the Insurance Institute for Highway Safety simulates a crash situation that is rare and extreme. The test used an extremely high crash severity which is unlikely to occur in real world crashes. In fact, less than 1% of all crashes fall within these parameters.” He added, “For the past decade, smart has a proven track record of safety with approximately one million cars on the road in 37 countries.”